1. Field of the Invention
This invention relates to drill bits for drilling oil and gas wells and more particularly, to polycrystalline diamond compact (PDC) drill bits, including core bits, which are provided with projecting, spaced, curved blades oriented in a forward sweep or curvature with respect to the center of the bit, such that cylindrical cutting elements mounted in the blades cut the drilling interval and divert and channel the flow of drilling fluid in an optimum manner. In a most preferred embodiment the cylindrical cutting elements are embedded in the blades at a selected back rake and side rake and are each shaped to define a dual bevelled cutting edge disposed at selected bevelled angles with respect to the sides of the respective cutting elements. The forward sweep of the respective blades and cutting elements and the carefully selected back rake and side rake and dual bevel of the cutting elements at the cutting edge area facilitate optimum cutting efficiency, as well as superior channelling of well fluid pumped through the drill bit across the blades and cutting elements and through the annulus between the drill bit and the down-hole interval.
2. Description of the Prior Art
Drill bits, including core bits, have long been constructed of a molded and fixed matrix body fitted with projecting, spaced blades having cutting elements embedded therein in spaced, offset relationship to optimize cutting efficiency. The cutting elements of PDC drill bits are typically cylindrical in shape, constructed of an extremely hard and tough material such as carbide and industrial grade diamonds and are mounted in the blades at selected positions to facilitate optimum cutting of the interval as the blade rotates under pressure supplied by the weight of the drill string to which the bit is connected. The cutting elements are embedded in each of the blades in staggered relationship to facilitate a uniform wear pattern for all cutting elements, a factor which contributes to longer bit life. Furthermore, the cutting elements are designed to stabilize the bit downhole and minimize vibration during the drilling operation. Another desired feature of such bits is "whirl resistance" and uniform distribution or channelling of drilling fluid which is pumped through the drill stem and bit, past the cutting elements and blade and up through the annulus between the bit and the down-hole interval. A typical line of PDC drill bits is distributed by Hycalog, of Denver, Colo., and includes a molded, fired matrix body having spaced blades provided with embedded industrial grade diamond cutting elements.
One of the problems inherent in conventional drill bits and PDC bits in particular, is the lack of facility for efficiently channeling the drilling fluid flowing from the end of the bits across the blades and cutting elements in the proper direction and "sweep" to substantially clean the cutting elements of cuttings from the drilling interval. Accordingly, under circumstances where the cuttings are not substantially scoured from the cutting elements as the cutting elements cut into the drilling interval, the efficiency of the cutting elements during the drilling operation is reduced and drilling time is lengthened. Another problem with conventional drill bits is the less than optimum cutting efficiency presented when embedding the cutting elements in blades that are substantially vertically oriented with respect to the longitudinal axis of the drill bit body and have no forward sweep in the direction of bit rotation, measured from the center of the bit, and are embedded in the blades at an inefficient back rake and side rake angle, or no such angular mounting at all.
Accordingly, it is an object of this invention to provide a new and improved drill bit which is characterized by multiple, spaced blades having a forward sweep or curvature in the direction of drill rotation measured from the center of the bit and fitted with multiple cylindrical cutting elements arranged in an optimum cutting configuration.
Another object of this invention is to provide a PDC drill bit characterized by multiple, spaced blades embedded with cylindrical cutting elements, each having a shaped cutting edge perimeter characterized by a dual angle cutting configuration and seated at a selected back rake and side rake, to optimize cutting efficiency.
A still further object of this invention is to provide a new and improved PDC drill bit which is characterized by multiple, spaced blades each having a forward sweep in the direction of bit rotation extending from the center of the bit and fitted with cutting elements embedded therein in an optimum back rake and side rake cutting arrangement, which cutting elements are each shaped with a dual bevel and bevel angle configuration at the cutting edges for optimum cutting efficiency as the bit rotates.